The claim of a piece of writing is essentially the same as its thesis. The thesis, as such, will generally be presented in the first paragraph (if not the first few lines) of the text. When we look at the article, thus, the first paragraph mentions two things: a gorilla named Little Joe (the hook/attention getter) and that zoos do a good job at nurturing their animals. Readers can be safe to assume that the article will cover how zoos do a good job at nurturing because of how the last sentence within the introductory paragraph begins with “But less well covered was the very real success…” As such, the claim of this piece is that zoos succeed at nurturing the animals that live within their walls. Again, it’s important to remember how, generally, the thesis turns out to be the claim.